A bruise may appear after a blood draw if small blood vessels are damaged when the needle is inserted or if not enough pressure is applied after the needle is removed.

A blood draw (phlebotomy) is a process in which a healthcare professional inserts a needle into a vein, usually on the inside of your elbow or wrist, and removes blood from your body.

Side effects and complications are much less common than they were in the past.

However, some research suggests that bruising is still relatively common after a blood draw. This bruising is usually harmless and doesn’t require medical treatment.

But if your bruises are large or accompanied by bleeding elsewhere, it may be a sign of a more serious condition.

Keep reading to learn more about the causes, treatments, and prevention methods of bruising after a blood draw.

Bruising, also known as ecchymosis, happens when capillaries located just under the skin are damaged, leading to bleeding underneath the skin. The bruise itself is discoloration from the blood trapped under the skin’s surface.

Bruising after a blood draw may be due to bleeding under the skin, which can be caused by damaged blood vessels. As the needle is inserted, it may damage a few capillaries, leading to the formation of a bruise.

Several experts note that improper technique from the person drawing blood is the most common cause of bruising and other complications. For instance, they may:

  • insert the needle at the wrong angle
  • insert the needle too far beyond the vein
  • reposition you after the initial placement

In some cases, however, bruising may not be the fault of the person drawing the blood, as it’s not always possible to see smaller blood vessels beneath the skin.

If the person drawing blood has any difficulty locating a vein — for example, if your arm is swollen or your veins are less visible — it makes it more likely that blood vessels will be damaged. This may be referred to as “a difficult stick.”

The person drawing the blood will usually take the time to locate the best vein, but sometimes they aren’t successful on the first try.

Another reason a bruise may form is if the person drawing the blood doesn’t apply enough pressure on the puncture site once the needle is removed.

In this case, there’s a greater chance that blood will leak into the surrounding tissues, creating a bruise.

In some cases, using the wrong needle size for drawing blood may cause bruising.

A needle that’s too large may damage or puncture the blood vessel wall, resulting in bleeding in the surrounding tissues. A needle that’s too small may require the healthcare professional to try drawing blood multiple times, causing further damage.

According to the World Health Organization’s 2010 Guidelines on Drawing Blood, the most common needle gauge for all populations is 23.

The needle length for adults is usually 1 to 1.5 inches.

For people with smaller veins, such as infants, children, and older adults, a healthcare professional may use a butterfly needle, also known as a winged infusion set or a scalp vein set.

Research from 2016 suggests that butterfly needles may greatly reduce the risk of blood vessel damage during a blood draw. However, it’s important to note that bruising and other complications are still possible.

You may also be more prone to bruising during or after a blood draw if you:

Older adults may also bruise more easily as their skin is thinner and has less fat to guard the blood vessels from injury.

If a bruise forms after a blood draw, it’s usually not a cause for concern. However, if you notice bruising on other parts of your body or the bruise is very large, you may have another condition that could explain the bruising.

You can’t always avoid bruising after a blood draw. Some people just tend to bruise more easily than others.

If you’re scheduled to have blood drawn, here are a few steps you can take to prevent a bruise:

  • Avoid taking anything that can cause blood thinning in the days before your appointment and 24 hours after the blood draw, including over-the-counter NSAIDs.
  • Don’t carry anything heavy, including a handbag, using that arm for several hours after the blood draw. Lifting heavy objects may put pressure on the needle site and displace your blood clot.
  • Wear a top with loose-fitting sleeves during the blood draw.
  • Apply firm pressure once the needle is removed and keep your bandage on for a few hours after the blood draw.
  • Drink plenty of water and limit alcohol for 24 hours.
  • If you notice a bruise forming, apply a cold compress to the area of injection and elevate your arm to help speed up the healing process.

It’s important to tell the healthcare professional drawing blood if you bruise frequently from having blood taken. Be sure to also tell them if you have any medical conditions or you’re taking any medications known to cause issues with clotting.

Bruising after a blood draw will usually get better after 1 week.

However, if the bruise is large or you notice that you bruise easily, it may indicate an underlying health condition.

Consider speaking with a healthcare professional if you experience:

  • feelings of tingling or numbness in your arm, hand, or fingers
  • pain, swelling, skin discoloration, or bleeding at the site of the blood draw
  • unusual bleeding in other places, such as your nose, gums, urine, or stool
  • a lump at the site where blood was drawn

Bruises after a blood draw are fairly common and will usually go away on their own as the body reabsorbs the blood.

The bruise may be caused by damage to a few small blood vessels during the blood draw process, and is usually not the fault of the healthcare professional doing the draw.

The bruise may change in color from dark blue-purple to green, and then brown to light yellow over the course of a week or two before it goes away completely.